Lara Anton, a press officer with the Department, said in an email that “all suspected cases are sent to the CDC for review by their neurologists” and added “it takes about a month for them to review a case and make the determination of AFM.”

Anton also noted that AFM is not required to be reported in Texas. Therefore, the 10 cases counted as of October 16 reflect those that have been shared voluntarily and have been through the case status determination process with the CDC.

Health providers have been asked to report cases with symptoms consistent with AFM, so that research into what causes the illness can be conducted.

At least 62 cases have been confirmed in 22 states this year, and at least 65 additional illnesses in those states are being investigated, according to the CDC. Similar waves of the same illness occurred in 2014 and 2016.

CDC officials say they haven’t found the cause. Some possible suspects, such as polio and West Nile virus, have been ruled out. Another kind of virus is suspected, but it’s been found in only some of the cases.

“This is a mystery so far,” the CDC’s Dr. Nancy Messonnier said in a call Tuesday with reporters.

A dramatic disease

About 90 percent of the cases are children who have suffered muscle weakness or paralysis, including in the face, neck, back or limbs. The symptoms tend to occur about a week after they had a fever and respiratory illness.

It is “a pretty dramatic disease,” but fortunately most kids recover, Messonnier said.

The cases in 2014 and 2016 were partly attributed to particular strains of respiratory germs called enteroviruses, which spread the most in the summer and fall.

Most people infected with enteroviruses suffer only minor symptoms like cough and runny nose. And though enteroviruses have been detected in some paralysis cases, it hasn’t been found in others, CDC officials say.

Lacking an established cause, health officials confirm cases through a review of brain scans and symptoms.

About 120 confirmed cases were reported in 2014. Another 149 were reported in 2016. In 2015 and 2017, the counts of reported illnesses were far lower.

The cases this year seem to be spread across much of the country, as were the earlier two waves. But mysteriously no other country has reported the emerging every-two-years pattern seen in the U.S., Messonnier said.